Bath for heat-treating metals



Patented Dec. 30, 1924.

UNITED STATES PATENT OFFICE.

ARTHUR E. BELLIS, OF NEW HAVEN, CONNECTICUT, ASSIGNOR TO THE BELLIS HEAT TREATING COMPANY, OF NEW YORK, N. Y., A CORPORATION OF CONNECTICUT.

BATH FOR HEAT-TREATING METALS.

No Drawing.

To all whom it may concern:

Be it known that I, ARTHUR E. BELLIS, a citizen of the United States, and a resident of New Haven, county of New Haven, and State of Connecticut, have invented certain new and 'useful Improvements in a Bath for Heat-Treating Metals, of which the following is a specification.

This invention relates to an improved bath for heat treating metals and has for its primary object to provide a mineral salt bath of such composition that it will possess a very wide range of working temperatures without appreciable volatilization.

It is another important object of the invention to provide a metal heat treatment bath of the above character which will be non-hygroscopic so that corrosion or the formation of rust upon the metal surfaces will be obviated. It is a further object of the invention to provide a high temperature mineral salt bath which will possess a maximum degree of fluidity so that there will be rapid and uniform transmission of heat throughout the body of the bath, thus resulting in a uniform heating of the metal piece immersed therein.

I have found that the particular bath composition which I shall subsequently describe, is of special advantage in the annealing of metals such as steel, brass, bronze, copper, alloys of chromium, nickel, etc. and in a pending application Ser. No. 640,076 filed of even date herewith, I have described and claimed a new method of heat treating such metals and particularly steel wire in coil form, wherein this new bath composition is employed.

With the above and other objectsin view, the present invention consists in a mineral salt bath for use in the heat treatment of metalsand in the use of the particular mineral salt components in certain relative proportions as hereinafter stated.

In the heat treatment of metals and especially in the annealing of steel, it has heretofore been the practice in the art to heat the metal to the requisite temperature so as to effect the desired transformation in its physical structure, either in a lead bath or in a suitable furnace. In the practice of either of these methods, the heating of the metal to the desired temperature proceeds comparatively slowly and in both cases, it is impossible to obtain a uniform heating Application filed May 19,

1923. Serial No. 640,075.

of all parts of the metal structure'to the same temperature. Also, when a lead bath is employed,owing to its high viscosity, particles of the lead will tenaciously adhere to the surfaces of the metal after the piece is withdrawn from the bath so that parts of the metal article will be subjected to a prolonged heating. F or obvious reasons, this is quite undesirable since the metal piece will be of varying degrees of hardness, which in many cases would render the metal unfit for the intended use.

By means of the new salt bath which I shall presently describe, I obtain a much more rapid heating of the metal piece to an absolutely uniform temperature throughout its structure. This is of particular importance in the annealing of metals since it is essential that the metal shall possess in all parts thereof, the same degree of ductility.

In one embodiment of the invention I employ a mixture of two mineral salt components, one of which is a chloride and the other a carbonate. I have found in practice that potassium chloride and sodium carbonate are best adapted for use in a heat treat ment bath intended for the annealing of metals. Preferablyfl form an eutectic mixture of these components, or in other words, a mixture which possesses the lowest melting point temperature of any possible mixture of such components. Such an eutectic mixture consists of substantially 52% potassium chloride and 48% sodium carbonate.

A mineral salt bath composition of the above character possesses a very wide range of working temperatures and will withstand lon and continued use at temperatures as high as 2000 F. without appreciable vaporizatlon or sludge formation. A 95 characteristic feature of such a mineral salt bath composition is its great fluidity so that the entire body of the bath material contained in the pot or crucible may be very rapidly heated to a uniform temperature 100 with a minimum consumption of fuel. Obviously, since this bath possesses great fluidity, when the metal piece is lifted therefrom, the surplus bath liquid will immediately drain back into the pot or crucible. there is little loss of the material and it does not collect thereon in appreciable quantity at spaced points so that the metal article Will be heated in spots for a longer period of time than the remaining portions there- 1 Thus of as is the case in the use of a lead bath.

However, a very thin film of the bath material will remain upon the surfaces of the metal. This film serves to protect the metal against atmospheric oxidization. Since all parts of the metal have absorbed exactly the same amount of heat from the bath material, the rate of cooling of the metal article will proceed uniformly throughout its structure. By then washing the surfaces of the metal in an acid bath, such for instance as hydrochloric acid, the film of the bath material coatin the surfaces thereof and which is rea ily be easily removed.

While I have referred to my new bath composition as being particularly advantageous in the annealing of metals, it may also be employed for other purposes such as the hardening of stainless steel which reuires a temperature of about 1900 F. lhe high specific heat and great stability of the bath composition render it easily adaptable to these uses, whereas in the attempted use of other baths for such purposes, s'erious difli'culties have been encountered.

It is particularly to be noted that a bath composition consistingmof potassium chloride and sodium car mate is non-hygroscopic so that when the article is withdrawn from the bath there will be no collection of moisture from the atmosphere upon the surfaces thereof. Thus rusting or corrosion of the metal surfaces is obviated.

From the foregoing description, the nature of my present invention and its several advantages in practical use will be clearly understood. I have herein referred to the bath 'as consisting of certain specific mineral salt components combined in certain definite proportions. It may, however, be

ossible that certain of the advantageous eatures above referred to might be attained soluble in such acid, may 7 by means of mineral salt bath compositions consisting of specifically different though equivalent components and varying within certain limits in the relative proportions in which they are employed. It is, therefore, to be understood that I do not regard myself as necessarily limited to the use of the specific bath components in the exact proportions stated, but reserve the privilege of adopting all such legitimate variations thereof as may be fairly considered as within the spirit and scope of the'invention as claimed.

I claim:

1. A mineral salt bath composition for the heat treatment of, metals consisting of an essentially non-hygroscopic stable mixture of a chloride and a carbonate possessing a relatively wide range of working tempera tures without appreciable vaporization.

2. A mineral salt bath composition for the heat treatmentof metals consisting of an essentially non-hygroscopic mixture of potassium chloride and sodium carbonate.

3. A mineral salt bath for the heat treatment of metals,,consisting of an eutectic mixture of two mineral salt components, essentially non-hygroscopic, stable and capable of bein heated to a temperature of approximate y 2000 F. without appreciable vaporization.

4. A mineral salt bath composition for the heat treatment of metals consisting of an eutectic mixture of potassium chloride and sodium carbonate, essentially nonhygroscopic and capable of being heated to a temperature of approximately 2000 F. without appreciable vaporization.

In testimony that I claim the foregoing as my invention, I have signed my name hereunder.

ARTHUR E. BELLIS. 

